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The mixed metal oxide of Lida or Telpro anodes has a low
consumption rate, measured in milligrams per ampere-year. As a
result, the dimensions remain nearly constant during the life of the
anode, providing a consistently low resistance. Whether operating in
soil, freshwater, mud or seawater, mixed metal oxide coatings
demonstrate high chemical stability, even in environments with low pH values.
Unlike other impressed current anodes, MMO coatings are not
affected by the generation of chlorine.
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Tubular Anodes
Mixed Metal Oxide (MMO) tubular anodes are titanium tubes with a mixed
metal oxide coating. The mixed metal oxide is a crystalline,
electrically-conductive coating that activates the titanium and enables
it to function as an anode.
Anode Strings
An MMO "anode string" is comprised of electrical cable threaded through one or
more tubular anodes. Electrical connection between the anode and cable is via a
patented crimping process. The crimp connection seals the anode around the cable
at both ends.
The terminal anode, the last anode on a string
assembly, has a metal loop for attaching a weight. Since only a single cable
lead protrudes from the hole, the junction box is eliminated when using a MMO
string - reducing the cost of materials and labor. String assemblies are also
available in a looped configuration with two tails, or as multiple, staggered
strings for system redundancy and maximum current distribution throughout the
ground bed. Like any impressed current anode, proper ground bed design is
paramount to optimum, low resistance performance. MMO anode manufacturers
recommend quality conductive, carbonaceous back fill, a vent pipe and
Centralizers, suitable cable, and good design practices.
Cable Selection
MMO
manufacturers recommend dual-insulated cable, such as
PVDF/HMWPE cable for use where anodes operate in ground beds high
in chlorides. Where chlorides are not anticipated, such as shallow vertical and
horizontal surface beds, an economical cable choice is HMWPE. The
high current capacity (150 amps) and flexibility of the EPR/CSPE cable
makes it ideal for seawater applications. EPR/CSPE is not recommended for
ground bed applications where chlorides are present (e.g., deep anode ground
beds).
MMO Wire Anodes
MMO
wire anodes are copper cored titanium wire with mixed metal oxide coating. The
mixed metal oxide is a crystalline, electrically-conductive coating that
activates the titanium and allows it to act as an anode.
MMO Disk Anodes
The MMO Disk Anode was developed for cathodic
protection of dam and navigation lock gates. Since our disk anodes are
designed to operate in fresh, brackish and seawater environments, other
suitable applications include: marine structures, water tanks and vessels.
With an optional primary seal spacer gasket, it can be used on the inside of
pipes, tanks, or other curved surfaces. The active element in the Disk Anode is
a 6" diameter x 1/8" thick titanium disk with a mixed metal oxide
coating. When applied on titanium, the MMO coating has an extremely
low consumption rate, measured in terms of milligrams per year. As a
result of this low consumption rate, the dimensions of the anode
remain nearly constant throughout the design life.
The mixed
metal oxide coated disk is secured into a 12" diameter x 1/8" thick
dielectric shield made of a durable, chlorine resistant, molded
FRP-vinyl ester. This FRP shield has been designed to resist damage
from floating debris and ice, as well as serving to enhance the
current throwing capability of the disk. The shield also minimizes
excessive current damage to the coating on surrounding steel. The
low profile Disk anode fits flush with the surface, so total
protrusion from the steel bulkhead is a mere 1/2".
The coated
titanium disk and shield assembly is attached to a 1-1/4" diameter
FRP stud via an interlocking epoxy joint. This joint enhances torque
capability and subsequent sealing. A 100% compressible EPDM
elastomeric o-ring molded into the shield assures a watertight seal
between the disk and steel bulkhead, while simultaneously allowing
the shield to fit flush against the bulkhead. Rod threads are
platinum plated to prevent oxidation of the titanium-providing a low
and constant contact resistance over the life of the anode. Nickel
plated brass nuts further ensure a reliable, low resistance contact.
And to prevent crevice corrosion of the titanium disk, a special,
mixed metal oxide coating has been applied on the edges and back.
Condenser anodes are available either bare, coated with a plastisol (PVC)
coating or with a specially designed molded Polypropylene box used to improve
current distribution and increase the effective life of the anode.
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